1995 Outrage 17 Engine Mounting Height

Optimizing the performance of Boston Whaler boats
ScottinLA
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1995 Outrage 17 Engine Mounting Height

Postby ScottinLA » Fri Dec 27, 2019 9:59 am

I've been looking at the engine height on my 1995 Outrage I 17'. The [anti-ventilation] plate is level with the keel.

Read a post from Phil T that the plate should be 1.5-inches higher than the keel. Before I go to the trouble of raising and testing, I want to confirm my understanding.

The engine is a Suzuki DF90 -that weighs 408-lbs. I have moved the batteries to the console to help, but the stern still sits low.

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Phil T
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Re: 1995 Outrage 17 Engine Mounting Height

Postby Phil T » Fri Dec 27, 2019 11:26 am

Good morning Scott

The typical engine, back in the day, was mounted so it sat on the transom. This was safe and easy. Over the years, some, not all, owners and dealers have discovered that raising the engine can increase performance and handling with no cost. The less engine in the water means less drag. The height raised is determined by several factors that include:

  • hull design
  • type and pitch of prop
  • loading of the boat (light or heavy)
  • typical sea state
  • activity type (cruising, watersports)
The standard recommendation to Boston Whaler owners for hulls larger than 13-feet is to mount the engine two-holes-up (assuming holes are drilled following the BIA pattern) unless one of the factors above is in play.

On my 1991 Outrage (repowered just before I bought it), the dealer mounted the engine one-hole-up (top bolt in the second hole from the top, one empty hole above the bolt). He installed a Yamaha painted stainless steel propeller. I raised the engine myself two additional holes. This move added 300-RPM to the WOT engine speed and gained 3 to 4-MPH in boat speed.

The boat did not perform as well in choppy small-craft-advisory (SCA) conditions and in high speed turns offshore--the propeller ventilated. Since I ran the boat in those conditions a lot of the time, I dropped down one-hole so the engine was two-holes-up. The ventilation was no longer a problem and I still added 150 to 175-RPM and 2 to 3-MPH. The WOT engine speed was 5,900-RPM, close to the 6,000-RPM recommended by the engine manufacturer.

As you may have also read, the Outrage 17-I boat does not like heavy engine weights. My prior Outrage 17-I had a Yamaha F115 which was 405 lbs. Adding the five quarts of oil, the stainless propeller, and rigging means about 420-lbs. I, too, moved my battery and all items of weight forward, and I only stored life vests in the stern quarter seats.

I plugged all the drain holes: two on deck and two in the splash well. I sealed the open seam between splash well rear wall and the molded stern surround.

To keep from shipping water in the stern, be gentle in transitioning to reverse as the initial movement causes the stern to squat. I also upgraded my bilge pump and discharge hose diameter to help evacuate water that came aboard.

I liked my boat so much that after selling it and moving south, I bought a 1992 model that is under overhaul re-power.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

biggiefl
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Re: 1995 Outrage 17 Engine Mounting Height

Postby biggiefl » Fri Dec 27, 2019 12:26 pm

Suzukis like to be raised high. I would try 3" above keel and go lower from there. I usually mount my Suzukis all the way up and they are great.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

ScottinLA
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Re: 1995 Outrage 17 Engine Mounting Height

Postby ScottinLA » Fri Dec 27, 2019 5:32 pm

The engine on the 1995 OUTRAGE 17 is mounted two-holes-up. I have not noticed the propeller blowing out. The boat really only gets used to chase and tow small sailboats on the lake. Thanks.
Last edited by ScottinLA on Sat Dec 28, 2019 8:21 am, edited 1 time in total.

ScottinLA
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Re: 1995 Outrage 17 Engine Mounting Height

Postby ScottinLA » Sat Dec 28, 2019 8:07 am

engine.jpg
View of engine mounting for the engine under discussion that shows the engine mounted two-holes-up as was described in a prior post.
engine.jpg (3.47 KiB) Viewed 5761 times

jimh
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Re: 1995 Outrage 17 Engine Mounting Height

Postby jimh » Sat Dec 28, 2019 8:11 am

ScottinLA wrote:I want to confirm my understanding [of proper engine mounting height]


SCOTT--I cannot confirm your understand of proper engine mounting height on the basis of vertical distance between the boat keel and the anti-ventilation plate.

Engine mounting height is generally NOT described or measured on the basis of the vertical distance from the hull's keel to the anti-ventilation plate.

The usual method is to describe the engine mounting in terms of the relationship of the engine to the transom with respect to which set of mounting holes has been used. Please see the article at the top of the listing of topics in this forum for more information about engine mounting height description using the number of holes-up from lowest. See a thorough explanation with illustrations at

ENGINE MOUNTING HEIGHT
http://continuouswave.com/forum/viewtopic.php?f=7&t=739

Engine mounting height is usually observed on the basis of where the anti-ventilation plate is located with respect to the flow of water around the engine gear case while the boat is on plane and the engine trim is set for the anti-ventilation plate to be parallel to the water surface. The general rule is the anti-ventilation plate should be running at the top of the water, or if the propeller permits, for the anti-ventilation plate to be running just above the top of the water.

Engine mounting height is usually assessed on the basis of how well the propeller avoids ventilation or loss of thrust, particularly during high speed operation, during turns, and during rough sea conditions.

Image
Fig. 1. View of the anti-ventilation plate position, with the plate running just at the top of the water, but not dry.

Image
Fig. 2. Overhead view of engines with their anti-ventilation plates running above the top of the water.

Image
Fig. 3. On black engines, observing the anti-ventilation plate position relative to the flow of water around the gear case is easier to see.

Running an outboard engine with elevated mounting height may provide a benefit of reduced drag due to less immersion of the gear case into the water. Exactly how high a particular engine with a particular propeller on a particular boat can be raised from the lowest mounting will be determined by the particulars of the engine, propeller, and boat, and by the type of operation of the boat. As mentioned, if the boat only runs in very calm water and the goal is the highest possible speed, a higher engine mounting may be useful. If the boat operates in rough seas with high waves, a lower mounting may be more appropriate.

ScottinLA
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Re: 1995 Outrage 17 Engine Mounting Height

Postby ScottinLA » Sat Dec 28, 2019 7:02 pm

Thanks. I get how the height is described.

My original question was to Phil because I read a post he wrote regarding the relationship of the plate and keel bottom. And he has experience with this hull, not just boats in general.

jimh
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Re: 1995 Outrage 17 Engine Mounting Height

Postby jimh » Sun Dec 29, 2019 8:45 am

Unless an engine is mounted to an adjustable mounting bracket with a jack screw, often called a jack plate, the engine height is not adjustable in small increments; the engine can only be moved up or down in steps of 0.75-inch. There is some variation among engine brands in the particular distance between the anti-ventilation plate and the engine mounting holes, and there can be variation in the location on the transom of the engine mounting holes.

With the variables involved and the constraint of movement only in 0.75-inch increments up or down, aiming for a precise distance between keel and anti-ventilation plate may be hard to achieve.

A starting point on a typical Boston Whaler boat is to mount the engine one-hole-up, and then see what occurs, that is, run the boat, look at the water flow, and assess how the propeller and the engine cooling system tolerate the mounting height.

If the engine mounting height is altered several times in trying to find the perfect height, be sure to properly seal the engine mounting bolts when testing is done. The lower engine mounting bolts will generally be submerged all the time the boat is in the water, and those holes must be completely sealed to prevent any ingress of water into the transom.

I like to have my boat set-up well and performing well, but at some point, the testing and trials end, and then we just go boating. Did we miss 0.5-MPH of more boat speed or 100-RPM of more engine speed? Maybe, but since the amount of time running at full-throttle is less than 1-percent of the engine operating time, I really don't worry about it.

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Re: 1995 Outrage 17 Engine Mounting Height

Postby jimh » Sun Dec 29, 2019 5:31 pm

SCOTT--what engine are we discussing? Based on the picture showing the engine has five mounting holes, I suspect it may be a Mercury. The older OMC engines usually only have a set of four mounting holes.

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Re: 1995 Outrage 17 Engine Mounting Height

Postby biggiefl » Mon Dec 30, 2019 10:23 am

Jim...original post states Suzuki DF90.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

jimh
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Re: 1995 Outrage 17 Engine Mounting Height

Postby jimh » Mon Dec 30, 2019 10:34 am

NICK--thanks. I reread the thread looking for that and did not see it. I am getting new reading glasses. The black engine led me to think Mercury.

That the Suzuki DF90 has mounting holes in a set of five is interesting. I noticed the new Evinrude G2 engines have five-hole mounts, too. It must be the new normal.

If the DF90 is already mounted two-holes-up as mentioned and illustrated, then what now is the distance between the keel and the anti-ventilation plate?

Since there is a comment about needing to move the engine, I am presuming the anti-ventilation plate on the engine is presently not 1.5-inches higher than the keel, the original dimension of engine height mentioned as a target. Does the engine need to go up or down to meet the 1.5-inch specified dimension?

ScottinLA
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Re: 1995 Outrage 17 Engine Mounting Height

Postby ScottinLA » Tue Dec 31, 2019 10:24 am

I wrote:The [anti-ventilation] plate is level with the keel.


Phil made a post some time ago in another thread stating that his Outrage 17 (same boat as mine) liked the plate to be 1.5" higher than the keel. The whole point of this thread was to confirm my understanding of his statement.

There is no specific "need" to raise the motor. Just something to consider as I continue sorting this boat out.

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Re: 1995 Outrage 17 Engine Mounting Height

Postby jimh » Tue Dec 31, 2019 2:21 pm

Oops--again I see I asked for information that was in the initial post. My apology for not reading over the thread more closely.

I am surprised that with the engine mounted two-holes-up the keel of the OUTRAGE 17 and the anti-ventilation plate of the Suzuki DF90 are in the same plane, that is, level with each other. If the goal were to raise the anti-ventilation plate to be 1.5-inches above the keel, the engine would need to be raised 1.5-inches or "two-holes" and would then be mounted four-holes-up. While there may be some situations where mounting four-holes-up might be desired, four-holes-up seems awfully high to me.

Here is an illustration I annotated using a photo of an engine mounted to a Boston Whaler boat ( a REVENGE 22 W-T Whaler Drive) that shows the relationship of the various elements of the boat and engine:

Image
Fig. 4. Originally from http://continuouswave.com/whaler/refere ... ingle.html,
showing vertical and horizontal distances between engine and boat with a Whaler Drive
with the engine mounted in the lowest position.


As seen above, the anti-ventilation plate is 2.5-inches above the keel of the hull, but also 35-inches aft of the transom. Later I changed to another engine, and raised that engine mounting one-hole or 0.75-inches up. So at present the anti-ventilation plate is about 3.25-inches above the keel of the hull. At present, the propeller shaft is 4.75-inches below the keel. The propeller diameter is 15-inches or 7.5-inch radius, so the tip of a propeller blade when vertical is then 2-inches above the keel.

ScottinLA
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Re: 1995 Outrage 17 Engine Mounting Height

Postby ScottinLA » Tue Dec 31, 2019 4:16 pm

keelToAVPlate.jpg
Fig. 5. The anti-ventilation plate position relative to the keel: they are level.
keelToAVPlate.jpg (21.08 KiB) Viewed 5575 times


I could go up one-hole or two-holes higher and be consistent with Phil’s experience [of the anti-ventilation plate being above the keel by 1.5-inches]

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Re: 1995 Outrage 17 Engine Mounting Height

Postby jimh » Fri Jan 03, 2020 8:48 am

As Figure 5 (above) shows, even at two-holes-up mounting the anti-ventilation plate of a SUZUKI DF90 is still just level with the hull keel.

I believe Nick remarked earlier that SUZUKI engines seem to need to be mounted higher than normal. Perhaps the SUZUKI notion of a particular shaft length is longer than other manufacturers, leading to the SUZUKI engine generally being mounted higher than one-hole-up or even two-holes-up to reach a effective engine mounting height.

If interested in further experimenting with engine mounting height, I suggest you try raising the engine. If you go to four-holes up, you can always easily lower the engine to three-holes-up if the propeller is not getting good thrust or if the engine cooling water pressure begins to falter.

Does the SUZUKI DF90 engine have a cooling water pressure gauge? If it does, note the cooling water pressure readings before you raise the engine, then compare them to the cooling water pressure readings when you have raised the engine. Also, monitor engine temperature, if the engine has a temperature gauge available.

Finally, before moving the engine mounting, go for a test run with someone who can take the helm while you lean over the transom and get a picture of the water flow over the anti-ventilation plate while the boat is running on plane and the engine is trimmed at the usual position so the plate is parallel to the water. Seeing where the water flow and the anti-ventilation plate align is really the best indicator of the engine mounting height.

If, at the present mounting height of two-hole-up with the DF90 on the OUTRAGE 17, the anti-ventilation plate is buried in the water, then you will have a basis to think about raising the engine.